The modern and future model for wireless data communication is the transmission of digital signals. The microwave radio frequency (RF) medium for carrying digital signals, however, remains analog. This presents some difficulties that remain a subject of continuing efforts to improve transmitter technology. Thus, while signal processing circuitry is often advantageously implemented in CMOS technology, wireless devices also typically include analog circuitry for encoding digital signals for transmission.
Transmitters thus remain an implementation conducted with analog circuits. Transmitters implemented with analog and RF electronics typically include a variety of functions. In many cases, the in-phase (I) and quadrature (Q) baseband signals are computed at baseband frequencies with digital signal processing (DSP), and subsequently converted to the analog domain with digital-to-analog converters (DACs) of moderate resolution (4-12 bits). The signals are subsequently up converted to RF, often via an intermediate frequency stage, using quadrature mixers and filters. A variable gain stage is often included. Finally, the transmitter typically comprises a power amplifier and an output coupler.
Due to the involved frequencies and the amount of data, the DAC implementations remain quite complex. Conventional digital transmitters and receivers require very high-speed digital-to-analog converters with high resolution. There accordingly remains a need in the art for improved encoding of data to wireless RF signals.